The present disclosure relates to a current-measuring circuit for redundantly measuring an electric current, having a measuring resistor, an evaluation circuit on an evaluation-circuit printed circuit board and a magnetic-field sensor.
The disclosure also relates to a battery having the current-measuring circuit according to the disclosure and to a motor vehicle having the battery according to the disclosure.
It would appear that, in future, new battery systems will be used both in stationary applications, such as wind turbines, in motor vehicles in the form of hybrid or electric motor vehicles, and in electronic devices, such as laptops or mobile telephones, with very stringent requirements being placed on said battery systems in respect of reliability, safety, performance and service life.
In vehicles with an at least partially electric drive, electrical energy stores are used in order to store the electrical energy for the electric motor which assists the drive or acts as drive. In vehicles of the most recent generation, in this case so-called lithium-ion batteries are used. These batteries are distinguished, inter alia, by high energy densities and an extremely low level of self-discharge. Lithium-ion cells have at least one positive and one negative electrode (cathode and anode, respectively) which can reversibly insert (intercalation) lithium ions (Li+) or extract (deintercalation) them again.
FIG. 1 shows how individual battery cells 10 can be assembled to give battery modules 12 and then batteries 14. This is performed by poles of the battery cells 10 being connected in parallel or series (not illustrated). In this case, by definition, a battery module 12 or a battery 14 comprises at least two battery cells 10, wherein the terms battery 14 and battery module 12 are often used synonymously. The electric voltage of a battery 14 is, for example, between 120 and 600 volts DC.
In the case of batteries for automobile drive technology (traction batteries), there is a need, to determine the state of charge and for reasons of safety, to measure the current supplied to and discharged from the battery cells. Therefore, the functionality of the current sensor must be known and hence be detectable by means of suitable measures. In many cases, the current is detected using current sensors which operate on the basis of the resistor principle (shunt). In order to keep the power loss in the shunt resistor to a minimum, the resistance value thereof is selected to be much smaller than that of the load. The small voltage drops arising therefrom must therefore be amplified for evaluation by means of electronic circuits connected downstream and evaluated. If the connection between resistor and evaluation circuit is interrupted, or if the resistor or the circuit has another fault, this cannot be readily unambiguously ascertained.
DE 10 2009 046 564 A1 discloses a battery system having a high-voltage system and a low-voltage system. The high-voltage system comprises a battery module, while the low-voltage system comprises a battery control unit (BCU). Cell-monitoring units are assigned to the battery cells and measure the voltages of the battery cells. Furthermore, the document discloses a redundant current measurement by means of a measuring resistor (shunt) and a Hall sensor.